What are the implications of a patient with end-stage renal disease (ESRD) and on dialysis, who still produces a small amount of urine, and how should their treatment be managed?

Management of ESRD Patients with Minimal Urine Output

For ESRD patients on dialysis who still produce small amounts of urine, preserving this residual renal function is critical as it independently reduces mortality risk and should be actively protected through appropriate medication management, optimized dialysis dosing, and avoidance of nephrotoxic insults. 1

Clinical Significance of Residual Urine Output

The presence of residual renal function (RRF), even at minimal levels, provides substantial survival benefit in hemodialysis patients:

• Mortality reduction: Patients with any measurable RRF have a 56% lower mortality risk (odds ratio 0.44) compared to anuric patients, independent of dialysis adequacy, age, diabetes, or cardiovascular disease status. 2

• Quality of life benefits: Residual urine output allows greater fluid intake flexibility, reduces interdialytic weight gains, and decreases the severity of volume overload between treatments. 1

• Dialysis adequacy contribution: RRF provides continuous solute clearance between intermittent dialysis sessions, complementing the clearance achieved during treatments. 1

Dialysis Prescription Modifications

When patients maintain measurable urine output (>200 mL/24 hours), dialysis dosing can be reduced while maintaining adequate clearance:

• Target single-pool Kt/V of 1.4 per session with minimum delivered 1.2 for thrice-weekly hemodialysis, but this dose may be reduced if significant RRF is present (typically defined as renal urea clearance >2 mL/min). 1

• Measure RRF periodically through 24-hour urine collections to calculate renal urea and creatinine clearance, ensuring dialysis dose adjustments remain appropriate as RRF changes over time. 1

• For patients with RRF <2 mL/min, prescribe minimum 3 hours per hemodialysis session. 1

Strategies to Preserve Residual Renal Function

Active preservation of RRF requires specific interventions, as the rate of decline can be substantially slowed:

Diuretic Therapy

• Loop diuretics at escalating doses preserve urine output in hemodialysis patients: Case series data demonstrate remarkably slow decline in urine volume (1 mL/month between 6-12 months) and GFR (0.03 mL/min/1.73m²/month) when furosemide is titrated up to 360 mg/day. 3

• Loop diuretics require higher doses in ESRD due to pharmacokinetic changes with diminished renal clearance, but provide benefits for volume management, hypertension control, and hyperkalemia prevention. 4

• Continue diuretics in dialysis patients with any urine output rather than reflexively discontinuing them at dialysis initiation. 4

Medication Management

• ACE inhibitors reduce RRF loss by 32% (adjusted odds ratio 0.68), making them first-line antihypertensives for dialysis patients with residual function. 5

• Calcium channel blockers reduce RRF loss by 23% (adjusted odds ratio 0.77), providing additional renoprotection. 5

• Avoid nephrotoxic agents including aminoglycosides systemically, NSAIDs, and radiocontrast when possible. 6

Dialysis Modality Considerations

• Peritoneal dialysis is associated with 65% lower risk of RRF loss compared to hemodialysis (adjusted odds ratio 0.35), though this should not override other clinical considerations for modality selection. 5

• High-flux hemodialysis with biocompatible membranes and ultrapure dialysate preserves RRF better than conventional hemodialysis. 1

Volume and Blood Pressure Management

Achieving true dry weight through adequate ultrafiltration is essential but must be balanced against hemodynamic stress:

• Target euvolemia through appropriate ultrafiltration at each session, dietary sodium restriction (typically <2 g/day), and lower dialysate sodium concentrations rather than high sodium dialysate or sodium profiling. 1

• Slower ultrafiltration rates minimize hemodynamic instability and may reduce ischemic injury to residual renal function. 6

• Monitor for lag phenomenon where blood pressure normalization may take weeks after achieving dry weight; persistent hypertension during this period should not be interpreted as inadequate volume control. 1

Risk Factors for Accelerated RRF Loss

Certain patient characteristics predict faster decline in residual function and warrant more aggressive preservation efforts:

• Female gender (45% increased risk), non-white race (57% increased risk), diabetes (82% increased risk), and congestive heart failure (32% increased risk) all independently accelerate RRF loss. 5

• Lower serum calcium levels correlate with faster RRF decline (19% increased risk per mg/dL decrease). 5

Monitoring Protocol

Systematic assessment of residual function guides treatment adjustments:

• Collect 24-hour urine volumes at dialysis initiation, then every 3-6 months to calculate renal urea and creatinine clearance. 1

• Define clinically significant RRF as urine output >200 mL/24 hours or renal clearance >2 mL/min. 1, 5

• Adjust dialysis prescription when RRF changes substantially to avoid both under-dialysis and excessive treatment time. 1

Common Pitfalls to Avoid

• Do not assume anuric status without measuring: Many patients maintain small but clinically meaningful urine volumes that are not apparent without collection. 1

• Do not discontinue diuretics reflexively at dialysis initiation: Loop diuretics provide multiple benefits beyond diuresis in patients with any urine output. 4

• Do not use standard dialysis dosing without accounting for RRF: Failure to measure and incorporate residual clearance leads to over-dialysis in some patients and under-dialysis in others. 1

• Do not expose patients to nephrotoxic insults unnecessarily: Each episode of acute kidney injury accelerates permanent loss of residual function. 1, 6